1. Field of the Invention
Embodiments of the invention relate to a transmission electron microscope (TEM) specimen and a method of manufacturing the specimen. More particularly, embodiments of the invention relate to a method of forming a dimple on a TEM specimen and a method of manufacturing the specimen.
This application claims priority to Korean Patent Application No. 2004-85576, filed on Oct. 26, 2004, the subject matter of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
In general, manufacturing a semiconductor device comprises several processes, such as a diffusion process, an oxidation process, a sputtering process, etc. These processes are performed repeatedly on a semiconductor substrate to stack layers on the substrate. A layer may be, for example, a metal layer such as an aluminum layer, a titanium layer, tungsten layer, etc., or an insulation layer such as a nitride layer, an oxide layer, etc. As semiconductor devices have become more highly integrated and their components have become increasingly smaller, the process of manufacturing a semiconductor device has become more complex.
When any one of the layers formed on a semiconductor substrate is defective (e.g., abnormally formed), the semiconductor device will typically fail to operate properly. In such circumstances, it is necessary to accurately and effectively analyze the defective layer, or at least determine whether the layer is defective or not. A TEM is often used to analyze a potentially defective layer. Conventional TEMs focus an electron beam on a specimen under examination to analyze a potentially effective layer in the specimen. An image of the layer under examination is obtained from the irradiating electron beam. More particularly, an electron diffraction pattern is obtained as the irradiating electron beam is diffracted by the constituent components of the layer being examined. In this manner, the conventional TEM analyzes the crystalline structure of the layer based on the resulting electron diffraction pattern.
To analyze a layer using a TEM, a suitable specimen must be properly prepared. There are many conventional methods and constituent processing steps involved in the preparation of a TEM specimen. Argon ion milling, chemical polishing, chemical etching, using a cleavage system, and electro polishing—all or individually applied to a specimen in accordance with the material properties of its stacked layers and the nature of the analysis point under examination—are typical method steps adapted to the preparation of a TEM specimen. Argon ion milling has been widely employed in the preparation of TEM specimens adapted to the examination of stacked layers formed on a semiconductor substrate and the interfaces between the stacked layers.
As noted above, a TEM obtains information about a specimen from an image generated by the transmission of an accelerated electron beam through the specimen. Thus, the specimen must be relatively thin, at least in the portion being specifically examined by the electron beam. In addition, the specimen must be prepared without scratches or contaminants. Thus, various methods have been studied to effectively prepare TEM specimens.
For example, one method of manufacturing a specimen for TEM examination is disclosed in Korean Patent No. 209658. According to the method disclosed in Korean Patent No. 209658, a rotational angle of the specimen is adjusted in accordance with a difference between average atomic weights for each of stacked layers or the difference between sputtering speeds used to fabricate each of the stacked layers. This ion milling process produces a specimen having a more uniform thickness, and may be completed in a relatively short time.
Another method of manufacturing a planar wafer specimen for testing is also disclosed in Korean Patent No. 253320. According to the method disclosed in Korean Patent No. 253320, marks on the planar specimen are used (e.g., visualized) in order to analyze the cross sectional state and surface state of a specific region in the wafer specimen (e.g., a specific layer formed on the wafer as captured within the specimen).
One conventional method of manufacturing a specimen comprises; a cutting process, a bonding process, a slicing process, a punching process, a grinding process, a dimpling process and an ion-milling process. In the cutting process, first and second preliminary specimens and first, second, third, and fourth dummy wafers are prepared. In the bonding process, a first face of the first preliminary specimen is formed on a first face of the second preliminary specimen. The first and second dummy wafers and the third and fourth dummy wafers are formed on second faces of the first and second preliminary specimens, respectively, to form a stacked specimen. The second faces of the first and second preliminary specimens are opposite the first faces of the first and second preliminary specimens, respectively. In the slicing process, the stacked specimen is cut using a diamond saw to form a rectangular specimen having a thickness of about 0.5 mm to about 1 mm. In the punching process, the rectangular specimen is punched to form a circular specimen having a diameter of about 3 mm. In the grinding process, both circular faces of the circular specimen are ground using a grinder or a polisher to form a final specimen having a thickness of no more than about 100 μm. In the dimpling process, a dimple is formed at a central portion of the final specimen so that the thickness of the central portion of the final specimen is no more than about 1 μm. In the ion-milling process, both sides of the final specimen are sputtered with argon ions to form a hole through the central portion of the final specimen, thereby completing the formation of the final specimen. The final specimen is held by a holder adapted for use with a TEM and is placed on a corresponding support. The hole of the final specimen is then visualized and analyzed.
Figure (FIG.) 1 is a cross sectional view illustrating a conventional TEM specimen.
Referring to FIG. 1, a first grinding region 20, a second grinding region 30, a third grinding region 40 and an ion-milling region 50 are formed concentrically around a central portion of a cross section of a specimen 10. Here, first grinding region 20 has a first diameter longer than a second diameter of second grinding region 30. The second diameter of second grinding region 30 is longer than a third diameter of third grinding region 40. Ion-milling region 50 has a fourth diameter shorter than the third diameter of third grinding region 40, and ion-milling region 50 is a hole used in observing specimen 10.
A conventional method of forming a dimple on a preliminary specimen is described in relation to FIGS. 2 to 4.
Referring to FIG. 2, a central portion of a cross section of a preliminary specimen 10′, formed by stacking wafers, is ground using a bronze wheel to form first circular grinding region 20 having the first diameter. Here, the formation of the first grinding region 20 is carried out until red light is observed in a transmission scope.
Referring to FIG. 3, the central portion of preliminary specimen 10′ is ground using a coarse wheel to form second grinding region 30 having the second diameter. Second grinding region 30 is concentric with first grinding region 20. Here, the formation of second grinding region 30 is carried out until orange light is observed in the transmission scope.
Referring to FIG. 4, the central portion of preliminary specimen 10′ is repeatedly ground using a fine wheel to form third grinding region 40 having the third diameter. Third grinding region 40 is concentric with first and second grinding regions 20 and 30. Here, the formation of third grinding region 40 is carried out until yellow light or white light is observed in the transmission scope.
FIG. 5 is a transmission scope picture illustrating a conventional specimen having a dimple.
Referring to FIG. 5, the red light serving as reference light in forming first grinding region 20 is exhibited in a first region I corresponding to an edge region of specimen 10. The yellow light serving as reference light in forming third grinding region 40 is exhibited in a third region III corresponding to a central region of specimen 10. The orange light serving as reference light in forming second grinding region 30 is exhibited in a second region II between first region I and third region III.
To analyze the cross section of specimen 10 using a TEM, a central portion of third grinding region 40, which is the thinnest portion of preliminary specimen 10′, is aligned with a central portion of preliminary specimen 10′ in forming the dimple. Here, an analysis region of specimen 10 has an allowable diameter of about 30 μm to about 50 μm.
However, when the central portion of third grinding region 40 is not aligned with the central portion of preliminary specimen 10′, the diameter of the analysis region of specimen 10 is smaller than the allowable diameter. Also, when hole 50 has a relatively large diameter, the analysis region in third grinding region 40 has a relatively small area.